What will happen in this scenario?
The VPC will modify the first subnet CIDR automatically to allow the second subnet IP range
It is not possible to create a subnet with the same CIDR as VPC
The second subnet will be created
It will throw a CIDR overlaps error
Explanations:
The VPC does not automatically modify the first subnet CIDR to accommodate a new subnet. Subnets within a VPC cannot overlap, and AWS does not auto-adjust CIDR blocks.
It is possible to create multiple subnets within a VPC, but the CIDR blocks for each subnet must not overlap. The VPC itself can have a broader CIDR (20.0.0.0/16) than the individual subnets.
The second subnet (20.0.0.1/24) cannot be created because its CIDR block overlaps with the first subnet (20.0.0.0/16). Overlapping CIDR blocks are not allowed.
The second subnet cannot be created due to the overlap in the IP range (20.0.0.1/24) with the first subnet (20.0.0.0/16). AWS will throw a CIDR overlap error.
In my opinion, the answer is:
It will throw a CIDR overlaps error